1. Field of the Invention
This invention relates to patient interfaces, particularly though not solely for use in providing Continuous Positive Airway Pressure (CPAP) therapy or positive pressure ventilation to patients suffering from obstructive sleep apnoea (OSA).
2. Summary of the Prior Art
In the art of respiration devices, there are well known a variety of respiratory masks which cover the nose and/or mouth of a human user in order to provide a continuous seal around the nasal and/or oral areas of the face such that gas may be provided at positive pressure within the mask for consumption by the user. The uses for such masks range from high altitude breathing (ie. aviation applications) to mining and fire fighting applications, to various medical diagnostic and therapeutic applications.
One requisite of such respiratory masks has been that they provide an effective seal against the user's face to prevent leakage of the gas being supplied. Commonly, in prior mask configurations, a good mask-to-face seal has been attained in many instances only with considerable discomfort for the user. This problem is most crucial in those applications, especially medical applications, which require the user to wear such a mask continuously for hours or perhaps even days. In such situations, the user will not tolerate the mask for long durations and optimum therapeutic or diagnostic objectives will not be achieved, or will be achieved with great difficulty and considerable user discomfort.
In common with prior art designs, is an inability to seal effectively when the user's face becomes distorted. For example, as shown in the prior art mask of FIG. 1 when the user 100 is sleeping on his or her side, one side 101 of the headgear tends to be pulled tight while the other side 102 tends to be loose. This causes the axis of the mask 103 to be twisted with respect to the axis of the head 104, due to the net torque from the headgear, resulting in leakage 105 on one side. The user 100 sleeping on his or her side may also distort the facial contours around the nasal area 106 and may lead to further leakage.